Bug 827976 - browser-places.js doesn't need to get a reference to the hidden window. r=mak

Differential Revision: https://phabricator.services.mozilla.com/D21080

--HG--
extra : moz-landing-system : lando

browser/base/content/browser-places.js

@@ -572,12 +572,12 @@ HistoryMenu.prototype = {
   },
 
   _getClosedTabCount() {
-    // SessionStore doesn't track the hidden window, so just return zero then.
-    if (window == Services.appShell.hiddenDOMWindow) {
+    try {
+      return SessionStore.getClosedTabCount(window);
+    } catch (ex) {
+      // SessionStore doesn't track the hidden window, so just return zero then.
       return 0;
     }
-
-    return SessionStore.getClosedTabCount(window);
   },
 
   toggleHiddenTabs() {